In factories producing thin-film solar cells, a pattering process is performed on a workpiece by using a laser machining device. The workpiece includes a glass substrate. On one surface of the glass substrate, a metal film or a semiconducting material film such as a silicon film is formed. In the patterning process, laser light is linearly scanned on the surface of such a thin-film layer of the workpiece, and thereby the thin-film layer is partially removed along a scanning line of the laser light. As a result, a straight groove (a scribe line) is formed.
Generally speaking, pulse laser light is applied as the laser light of laser machining devices for use in such a patterning process, because, for example, the use of pulse laser light makes micromachining possible and allows thermal influences to be readily reduced. In a case where pulse laser light is applied as the laser light, the laser light is scanned such that the irradiation range of the laser light oscillated at one timing partially overlaps, on the workpiece, with the irradiation range of the laser light oscillated one pulse width prior to the laser light oscillated at the one timing. In this manner, the continuity of the scribe line is assured. It should be noted that an area where the irradiation ranges of the laser light of such adjoining two pulses overlap each other is called an “overlap margin”.
There is a known conventional laser machining device configured to reflect laser light from a deflector by means of a mirror fixed on an are, such that the laser light reflected by the mirror fails on a workpiece (see Patent Literature 1, for example). In this laser machining device, the deflection center of the deflector is positioned at the center of the arc. This configuration is intended to cause the laser light to be incident on the workpiece substantially perpendicularly regardless of a rotation angle of the deflector, and make the length of an optical path from the deflection center to the workpiece substantially constant regardless of the rotation angle of the deflector. A camera is disposed such that its image-capturing axis is coaxial with the beam of the light. The position and output of the laser light are controlled based on position and type information about the workpiece, the information being obtained from an image captured by the camera. On the workpiece, a mask may be placed in an area where the laser light falls on, and thereby a wide variety of machining can be performed.